#include<stdio.h>
double count(double m);
int main()
{   double i,su=0,number;
	scanf("%lf",&number);
	for(i=1.0;i<=number;i++)
	{
		su=su+count(i);
	}
	printf("%lf",su);
	return 0;
}
double count(double m)
{   double sub;
	sub=(1/m)*(1/(m+1));
	return sub;
}
